Connecting a first and second member releasably using threaded studs is known.
The first member may for example be an aluminium or magnesium housing, and the second member a helicopter lubricating oil tank casing.
Threaded studs are known which substantially comprise:                a first thread which screws onto a first nut screw on the housing;        a second thread onto which screws a lock member such as a nut; and        a non-threaded portion between the first and second thread and which fits loosely through a seat in the casing.        
The nut is screwed to connect, and unscrewed to disconnect, the housing and the casing.
When screwing and unscrewing the nut, friction between the nut thread and the second thread may also result in undesired rotation of the stud with respect to the housing.
To prevent this from happening, toothed cadmium-plated steel lock washers are employed.
More specifically, the toothed washer is housed inside a seat on the housing, and comprises a first and opposite second toothed surface.
The radially inner first surface of the washer engages teeth on the stud, which are housed inside the seat, are interposed axially between the first thread and the intermediate portion of the stud, and comprise a number of teeth coaxial with the longitudinal axis of the stud.
Because the toothed lock washer is made of steel, i.e. harder material than the aluminium or magnesium the housing is made of, the radially outer second surface of the washer forms teeth on the inner surface of the seat on the housing.
The stud is thus prevented from rotating with respect to the housing by the friction produced between the second surface of the washer and the seat on the housing, and between the first surface of the washer and the stud teeth.
The second surface of the toothed washer cutting into the seat on the housing may produce microcracks.
A need is felt within the industry to minimize the risk of microcracks forming on the housing.
Contact between two dissimilar materials, such as the steel of the toothed washer and the aluminium/magnesium of the housing seat, may also initiate corrosion phenomena.
A need is felt within the industry to minimize the risk of initiating corrosion phenomena.
Finally, to remove the stud, e.g. in the event of damage, the toothed washer must also be removed.
This calls for the use of a production milling machine or, if the stud is also assembled, a special cutter fitted to a hand-drill.
A need is felt within the industry for a simple, low-cost way of removing studs with no need for complex tools.